The present invention concerns, in general, the correction of vision by insertion of a corrective element in the eye and, more specifically, the correction of presbyopia.
According to new theories, presbyopia is not linked solely to the loss of flexibility of the crystalline lens on aging, but is mainly due to increase of the diameter of said crystalline lens with age.
As schematically represented in FIG. 8, the crystalline lens Cr contained in the crystalline lens sac S is suspended from the sclera Sc along a ring of the latter located behind the limbus L separating the vitreous body V from the opaque body O. This ring is, on the average, situated at a latitude spaced from 2 to 3 mm apart from the limbus, if the optical axis is taken as reference. Said suspension of the crystalline lens is secured by a ligament Z called zonule attached to the ciliary body Cc. As the size of the scleral ring and ciliary body Cc do not vary in time, the zonule Z is gradually expanded in the course of enlargement of the crystalline lens Cr and partially loses its traction power on the equator of the crystalline lens sac S.
A new surgical method has therefore been proposed to correct presbyopia, consisting of increasing the diameter of the scleral ring in the ciliary body, so as to stretch the zonule, which will again be able to perform its function of deformation of the crystalline lens under the effect of contraction of the ciliary muscle and return the power of accommodation to the eye.
For the use of this method of treatment, Schachar proposed a truncated cone-shaped ring set in place by suture around the scleral ring (U.S. Pat. No. 5,465,737).
However, this ring requires a very long and difficult surgical intervention and entails unpleasant sequelae for the patients.
Arched segments have therefore been recently proposed, which are set in place in loops incised in the thickness of the sclera concentric to the limbus, perpendicular to the ciliary body, and which constitute stiffeners exerting an outward traction stretching the zonule. In practice, four scleral segments are placed at 90xc2x0.
This intervention is much more effective than placement of the complete ring initially proposed by Schachar, for the surgical procedure is simple and rapid (incision of four tunnels constituting the loops and insertion of the segments) and eliminates any suture, therefore considerably diminishing the patient""s discomfort and operating sequelae. This technique is schematically illustrated in FIG. 9.
This figure shows a sclera fragment Sc, in which a tunnel T has been formed, like a belt loop.
The segment Sg has been inserted in this loop and rests at its bases A and B on the sclera, on which it bears, while its bridge C exerts an outward traction force. It can be seen that the zonule is expanded Z1 perpendicular to force C and relaxed Z2 perpendicular to forces A and B.
However, the present segments, which are simple cylindrical rods, present a sizable risk of perforation of the sclera by reason of the fact that they punctually bear on the latter.
The purpose of this invention is to eliminate this disadvantage and to propose scleral expansion segments which present no risk of perforation of the sclera.
According to the invention, the scleral expansion segment which, in a manner known per se, consists of an arched rod designed to be placed on the sclera perpendicular to the ciliary body, is characterized in that its free ends have a spatula shape wider than the diameter of said rod, so as to constitute wide support bases.
The segment according to the invention is further remarkable in that:
the bases have a radius of curvature R1 corresponding to that of the sclera perpendicular to the ciliary body, while the bridge has radius of curvature R2 less than R1;
it presents a multitude of perforations;
it is coated with a biocompatible synthetic material with porous surface;
it consists of a core of deformable material with shape memory, sunk in a layer of soft material;
it has an internal canal designed for placement of a core, the nature and strength of which can be chosen in order to adjust the effect of the scleral expansion segment;
the core consists of an injectable product;
it is made in two parts interlocking with each other;
the segment consists, on one side, of a bridge, one end of which is integral with a base, and, on the other, of a removable base, and in that complementary means of attachment are placed between the free end of the bridge and the removable base; and
the two parts contain means for preventing any rotation in relation to each other.